Cardiovascular magnetic resonance imaging (MRI) is the gold standard for assessment of cardiac function but image quality is compromised in patients with severe arrhythmias. The retrospective CINE technique is standard for clinical cardiac MRI. In this technique, a fast MRI sequence is coordinated with retrospective ECG gating to synthesize data from multiple heartbeats into a single beat representing the composite cardiac motion. Using this technique, numerous short time frames are evenly produced in the cardiac cycle. However, the CINE technique is limited when imaging patients with cardiac arrhythmias. FIG. 1 illustrates several failure modes of this ECG-based retrospective reconstruction. If ectopic beats are detected by the trigger mechanism, there are two possible outcomes. If arrhythmia rejection (AR) is off, then the ectopic beats will be incorrectly scaled to the desired retrospective reconstruction (RR) duration leading to corrupt imaging data (crosshatch pattern). If AR is on, data will be rejected leading to prolonged scan times and unachievable breath holds. If the ectopic beats go undetected, k-space data will be acquired during the ectopic beats and will either be scaled, rejected, or a combination leading to imaging artifacts.
Real-time MRI methods cannot generate images with temporal and spatial resolution comparable to a multi-shot or segmented data acquisition since acquisition of MRI data is slow relative to cardiac motion. However, low-spatial and high-temporal resolution images can provide useful information about the cardiac phase. A method to utilize these images for improved retrospective reconstruction is presented.